Known converter circuits comprise a converter unit having a multiplicity of actuatable power semiconductor switches which are connected up in known fashion for the purpose of switching at least two switching voltage levels. Each phase connection of the converter unit has an LCL filter connected to it. The converter unit also has a capacitive energy store connected to it, which is commonly formed by one or more capacitors. For the operation of the converter circuit, an apparatus is provided which has a control device for producing a hysteresis active power value, a hysteresis reactive power value and a selected flux sector which is connected to the actuatable power semiconductor switches via an actuation circuit for forming an actuation signal from the hysteresis active power value, the hysteresis reactive power value and the selected flux sector. The actuation signal is therefore used to actuate the power semiconductor switches.
A problem of a converter circuit as mentioned above is that the LCL filters can cause permanent distortion, i.e. undesirable oscillations, in the filter output currents and filter output voltages on account of resonant oscillations in the LCL filters, as shown in a common time profile for filter output currents in FIG. 3. In an electrical AC voltage system, which is typically connected to the filter outputs, or when an electrical load is connected to the filter outputs, such distortions can result in damage or even destruction and are therefore highly undesirable.